Monday, August 31, 2009

Today I installed an upgrade which contains a few small visual enhancements and a couple of bigger architectural changes under the hood. I hope the latter didn't break anything.

The callsign / object name labels shown on the map now have colours which partially match "APRS symbol attribute" colours in Bob Bruninga's original APRS software:

White: APRS stations which are capable of messaging

Gray: APRS stations which are not capable of messaging

Violet: Objects

Purple: Items

AIS stations have green labels and weather stations have yellow labels, although that conflicts with Bob's spec. I'm running out of colours and I don't have any idea which objects are sent by *you*. Hmm, well, maybe I could compare the source callsign with your aprs.fi login...

aprs.fi now updates the case of the callsign / target name to match exactly what is transmitted, even though the service is still case insensitive. So, if you're transmitting an APRS object named 'Oh7lzb' now, and you switch to a normal APRS station (not object) with the callsign 'OH7LZB', the service will now show the updated upper-case 'OH7LZB'. Before now, it retained the old mixed-case name. Both will refer to the same station and tracking history on aprs.fi, as before.

The path adviser on the info page now warns you about funny path elements like WIDE1-3.

The bigger under-the-hood changes make the web UI marginally quicker, easily expandable, and enable more fine-grained per-feature access control and site configuration.

Wednesday, August 26, 2009

During the weekend I replaced the date browsing menu with a new AJAX-based one. The downside is that the new one doesn't tell you how many positions were received during a year, month or day. The upside is that it's much, much faster than the old one. The old one was generated completely when you looked up a station on the map, which in turn required scanning the whole position history of the station, which caused a lot of disk IO, which filled up the caches. The new one just quickly checks whether there are any points during the year, month or day, and does it only when needed.

The new one only shows the days when new points have been inserted. For a fixed station like a digipeater it shows the initial date when the station was first heard by aprs.fi - the old one showed all of the days between the initial packet and the latest packet at the same position.

The info page now shows the latest telemetry from the station instead of the number of telemetry packets stored. It's much more useful and much quicker to look up.

Most importantly - there is now a GIF animation in a couple of places! Honestly, I never thought I'd bother with such an useless thing which takes such an enormous amount of time to produce. But I accidentally figured out how Gimp does it, so I just had to try it once. Sorry!

In case you were wondering - a new kitten arrived on Saturday evening! The photo is maybe a bit off-topic, but it sure is cuter than the computers and radios.

Sunday, August 16, 2009

Quick recap: A cargo vessel called Arctic Sea (MMSI 215860000) was probably hijacked on July 24th 2009 near the eastern coast of Sweden. This was big news in northern Europe, since hijackings generally happen near the Somali coast, not over here. The ship has a Russian crew of 15, it appears to be owned by a Finnish company, and the owners of that company are of Russian origin. The Finnish media had considerable trouble trying to figure out the true owners, and the owners were really hard to interview. The ship deported from the harbor of Pietarsaari on 22nd of July and carries 6500 tons of Finnish timber, worth of about 1.3 MEUR.

The really odd thing is that the ship didn't go to the nearest Swedish port, but continuedtowardsAfricaas ifnothing had happened. Very strange indeed. Either the hijackers were still on the ship, or the crew is taking part in the plot.

There have been a few questions about AIS positions of Arctic Sea shown on aprs.fi.

Q: Why is the track not shown for the moment of hijacking between Gotland and mainland Sweden?

A: There are no AIS receivers in the area which would directly send AIS reports to aprs.fi. These receivers are run by volunteers (thank you!), and each volunteer chooses where to submit AIS data. There is a receiver in the area, but it is submitting data to MarineTraffic only, and while MarineTraffic and aprs.fi exchange AIS data, aprs.fi is not getting the reports of all of those receivers. The Swedish maritime officials have an AIS receiver network of their own, and they've reported it ran circles and stopped for a while.

A: Technically, it's possible, but I personally would find it very unlikely. It is easy to fake and it doesn't make any sense for the hijackers to publish their true position like this.

The position report was sent by an anonymous receiver station to MarineTraffic. It is quite easy to send fake data to MarineTraffic over the Internet, since they allow unauthenticated UDP packets containing NMEA strings to be sent to the service. aprs.fi does not allow unauthenticated UDP packets, all AIS submissions are tied to a specific receiving station using a password. Of course any one of those stations could feed us invalid positions, but at least we have some idea of the originator.

If the hijackers (or someone else) wanted to play tricks, they could also go to a shop selling marine radio equipment, buy an AIS transmitter, configure Arctic Sea's MMSI number (and other correct data) in it, give it an incorrect position by crafted NMEA strings (fake GPS receiver on the serial port of the AIS transmitter) and have it transmit the packets on the correct AIS frequency. If they've got the money and motivation to hijack ships with guns and speedboats, they've certainly got the guts to buy or steal AIS equipment. They could also grab the AIS transmitter from Arctic Sea, and take it to another position using a speedboat.

The French navy says there were 3 military vessels in the claimed position on the Bay of Biscay, heading for the Baltic sea, and they didn't see the hijacked ship. And they didn't see it on their radar, either.

The coast guard of Kap Verde claims to have seen the vessel about 800 km off the coast of Cape Verde, which is some 3600 km away from the Bay of Biscay.